Upgrade ubuntu to 12.04

Ubuntu provides the flexibility of upgrading from an older version to a new supported version. You don't need to install it fresh to use  new Ubuntu this guide helps you to upgrade to Ubuntu 12.04 from an older version.You can directly upgrade to Ubuntu 12.04 LTS ("Precise Pangolin") from Ubuntu 11.10 ("Oneiric Ocelot") or 10.04 LTS ("Lucid Lynx").

Why upgrade

Why should you upgrade instead of performing a clean install of a supported version? Some don't like to perform new installations when there is a possibility to upgrade. The advantage of this is that you can keep your current configuration without having to change much. This is often the case in production environments where you don't want to lose a machine just because it needs a higher OS version.

Upgrade from 11.10 to 12.04 LTS and 10.04 LTS to 12.04 LTS

Network Upgrade for Ubuntu Desktops 11.10 to 12.04 LTS (Recommended)

You can easily upgrade over the network with the following procedure.

1. Run the Update Manager application from the Unity Dash
2. In Update Manager, click the Settings... button, and enter your password to start the Software Sources application.
3. Select the sub menu Updates from the Software Sources application.
4. Check the "Release upgrade - Show new distribution releases" drop down to make sure "Normal releases" is selected, and change it if otherwise.
5. Close the Software Sources application and return to Update Manager.
6. In Update Manager, click the Check button to check for new updates.
7. If there are any updates to install, use the Install Updates button to install them, and press Check again after that is complete.
8. A message will appear informing you of the availability of the new release.
9. Click Upgrade.
10. Follow the on-screen instructions.

Network Upgrade for Ubuntu Desktops 10.04 LTS to 12.04 LTS (Recommended)

Note that the page under https://wiki.ubuntu.com/PrecisePangolin/ReleaseNotes/UbuntuDesktop#Upgrading_from_Ubuntu_10.04_LTS_to_Ubuntu_12.04_LTS says: "It is generally recommended that users of Ubuntu 10.04 LTS wait until the first point release, due in July, before upgrading." Follow the instructions there if you want to upgrade earlier since the following instructions will probably not work until then.

You can easily upgrade over the network with the following procedure.

1. Open the Update Manager application from the System → Administration menu.
2. In Update Manager, click the Settings... button, and enter your password to start the Software Sources application.
3. Select the sub menu Updates from the Software Sources application.
4. Check the "Release upgrade - Show new distribution releases" drop down to make sure "Long term support releases only" is selected, and change it if otherwise.
5. Close the Software Sources application and return to Update Manager.
6. In Update Manager, click the Check button to check for new updates.
7. If there are any updates to install, use the Install Updates button to install them, and press Check again after that is complete.
8. A message will appear informing you of the availability of the new release.
9. Click Upgrade.
10. Follow the on-screen instructions. 

Upgrading Using the Alternate CD/DVD

Use this method if the system being upgraded is not connected to the Internet.

1. Download the alternate installation CD from http://releases.ubuntu.com/precise/
2. Burn the ISO to a CD and insert it into the CD-ROM drive of the computer to be upgraded.
   • If the ISO file is on the computer to be upgraded, you could avoid wasting a CD by mounting the ISO as a drive with a command like (please make sure that the path to the iso file in the second command reflects where you file is located in your computer, also the Desktop folder may have a different name if you are using Ubuntu in a language different than English):

     sudo mkdir -p /media/cdrom
     sudo mount -o loop ~/Desktop/ubuntu-12.04-alternate-i386.iso /media/cdrom

3. A dialog will be displayed offering you the opportunity to upgrade using that CD.
4. Follow the on-screen instructions.

If the upgrade dialog is not displayed for any reason, you may also run the following command using Alt+F2:

gksu "sh /media/cdrom/cdromupgrade"

Or in Kubuntu run the following command using Alt+F2:

kdesudo "sh /media/cdrom/cdromupgrade"

Upgrading from a Torrent

If you're familiar with torrents and have an ISP that doesn't limit them, you can download the upgrade much more quickly. You'll also be sharing your bandwidth with other Ubuntu users and helping to reduce the load on the servers, which is especially beneficial on release days when the server overload causes problems.

Just visit http://releases.ubuntu.com/12.04/, and download the appropriate torrent file for the alternate installation CD, found in the list towards the bottom of the page. (It will have a filename like ubuntu-12.04-alternate-i386.iso.torrent.) Load it into your BitTorrent client, and after it is done downloading the ISO, follow the alternate CD upgrade instructions.

Detailed instructions in a blog post and in a forum thread.